Environment
Fact-checked

At AllThingsNature, we're committed to delivering accurate, trustworthy information. Our expert-authored content is rigorously fact-checked and sourced from credible authorities. Discover how we uphold the highest standards in providing you with reliable knowledge.

Learn more...

What Causes Fog?

Fog forms when air near the ground cools enough for water vapor to condense into tiny droplets, creating a cloud at ground level. This can happen through various processes, such as radiational cooling on clear nights or when warm, moist air moves over cooler surfaces. Intrigued by how weather patterns influence fog formation? Discover the atmospheric secrets behind this misty phenomenon.
Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon

Fog is a meteorological phenomenon caused by a supersaturation of the air, so that it can no longer hold water vapor. The water vapor precipitates out into small droplets of condensation, or fog. The processes are similar to those which make clouds, although fog forms close to the ground, rather than higher up in the atmosphere. Because visibility can be limited in foggy conditions, care should be taken when driving or walking, especially since it tends to muffle and distort sound, potentially rendering people unaware of hazards.

Whenever the air reaches a point of extremely high humidity, fog occurs. Most commonly, it happens when the air rapidly cools, causing condensation to form. There are a number of types, named for the conditions which create them. Drivers who are navigating in it should use low beams or fog lights, rather than high beams, which will simply reflect from the water droplets and create glare.

Fog commonly occurs when air rapidly cools, causing condensation to form.
Fog commonly occurs when air rapidly cools, causing condensation to form.

Along the shores of oceans and large bodies of water, advection fog happens when moist air from the water passes over the cooler surface of the land. Frequently, warmer weather inland sucks the moist air across the land, creating a thick blanket of fog. This happens most frequently around the ocean because the salt increases the humidity, and condensation can form at a much lower humidity level around salt.

Care should be taken when driving or walking in foggy conditions.
Care should be taken when driving or walking in foggy conditions.

Another common type is radiation fog. This type usually occurs after dark, when the Earth radiates heat outwards. As the heat rises, it is cooled, causing saturation conditions. Radiation fog usually clings close to the ground, and disappears by mid-morning, once the day warms up enough to dissipate it. A variation on this, tule fog, is found in the Central Valley of California. Tule fog happens when cold mountain air sinks into a depression such as the valley at night. Warmer air above it presses the cold air down, causing fog to form and linger for days. This type occurs in the fall and winter, when conditions on the mountains are colder.

Freezing fog may cause ice crystals to form on trees.
Freezing fog may cause ice crystals to form on trees.

A rare type called ice fog can only be formed in extremely cold conditions such as those at the Arctic and Antarctic. When the ambient air temperature is substantially below the freezing point, but still humid, the water droplets which would normally form fog turn into small ice crystals instead. Ice fog can be dangerous to drive in, as the crystals cling to windshields and headlights.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...

You might also Like

Discussion Comments

anon251740

Interesting. This will help me in my research in school now.

anon66167

in addition to other causes light wind of 3-6 miles per hour is a must.

sevenseas

Radiation fog forms only on calm, clear and cool nights. If it is windy the air will be mixed up and prevent fog from forming.

Similarly if it is cloudy, fog will not form, because the clouds in effect blanket the earth, preventing the heat from escaping.

Post your comments
Login:
Forgot password?
Register:
    • Fog commonly occurs when air rapidly cools, causing condensation to form.
      By: Bikeworldtravel
      Fog commonly occurs when air rapidly cools, causing condensation to form.
    • Care should be taken when driving or walking in foggy conditions.
      By: artush
      Care should be taken when driving or walking in foggy conditions.
    • Freezing fog may cause ice crystals to form on trees.
      By: Stihl024
      Freezing fog may cause ice crystals to form on trees.
    • Fog fformation is similar to cloud formation, but fog forms close to the ground.
      By: veneratio
      Fog fformation is similar to cloud formation, but fog forms close to the ground.